The present invention relates to LPG fuel injection systems for internal combustion engines.
Fuel systems of this type are already known, as in European Patent EP-B-0 725 205 of the same Applicant and the corresponding U.S. Pat. No. 5,592,924. Additional patents relative to this field are patent EP-B-0 922 851, also of the same Applicant, and the corresponding U.S. Pat. No. 6,050,237.
According to the known technique, fuel systems of this type include:
a LPG fuel tank,
a number of injectors associated with the engine""s cylinders, for injecting liquid LPG into these cylinders,
a fuel manifold or rail for feeding LPG to the said injectors,
a line for feeding LPG from the fuel tank to the said rail,
a return line for returning LPG fed in excess to the injectors back to the fuel tank,
sensors for the level of LPG in the fuel tank,
a pump immersed in the fuel tank for delivering LPG via the LPG fuel line, and
an electric motor driving the pump.
The object of this invention is that of realizing a fuel system and method that, on the one hand, ensures that the fuel pump delivers the correct head and the correct flow rate under all engine running conditions, whilst on the other hand also ensuring a long operating life for the pump itself.
In order to achieve this objective, the object of the invention is a LPG fuel system having all of the above-indicated characteristics and also characterized in that the said system includes electronic means of pump control, a pressure sensor and/or temperature sensor inside the fuel tank, and by the fact that the said electronic means are programmed to:
keep the pump constantly running when the temperature in the fuel tank is below 0xc2x0 C. or above 80xc2x0 C.,
realize a chopper control on the voltage supply to the electric motor driving the pump when the temperature in the fuel tank is between 0xc2x0 C. and 80xc2x0 C.
In low-temperature engine running conditions, that is below 0xc2x0 C., low vapour pressure is registered for the LPG inside the fuel tank. The pump must provide the correct head to correctly feed the injectors (which typically require a 2-bar pressure hike). The electronic means take care of keeping the pump constantly running, controlling the supply current in order to guarantee the required head.
In high-temperature engine running conditions, that is above 80xc2x0 C., high vapour pressure is registered for the LPG inside the fuel tank, with the presence of vapour bubbles. In order to be sure that the LPG is always in the liquid state when injected into the engine""s cylinders, it is necessary that the pump delivers high flow, eliminating the vapour bubbles. The electronic means thus take care of keeping the pump constantly running, controlling the voltage in order to guarantee the pump""s power supply, thereby assuring the necessary flow rate. Always in accordance with the invention, under normal temperature conditions, that is between 0xc2x0 C. and 80xc2x0 C., the pump is not kept constantly running. In the case of a 100 HP internal combustion engine for example, a 60 1/hr LPG flow rate is required for feeding the injectors. When fed with a 12-volt supply, a typically used pump in a fuel system of this type is capable of guaranteeing a flow rate of 120 1/hr. A chopper control of the voltage can therefore be applied in such conditions to guarantee, on the one hand, feeding the injectors at an adequate flow rate and, on the other, maintaining the current absorbed by the pump at lower average values that prolong the useful lifetime of the motor-pump group.